Dragonfly Nymph Attacks Pregnant Mussels

For female freshwater mussels, reproduction is a stressful affair. Now zoologists have discovered an extra burden on pregnant Texas hornshell mussels, Popenaias popeii: an unexpected assailant that eats them away from within.

A mussel mom’s stresses start when her fertilized eggs enter tubes
within her gills and develop into glochidia, or larvae. The glochidia
reduce water flow, limiting her oxygen and food supplies. Eventually,
they enter a parasitic phase, and must relocate to a fish host. So the
female often casts her glochidia, embedded in a web of mucus, into the water, hoping that a fish will swim through and pick some up.

Throughout her pregnancy, the mussel is vulnerable to parasitic
mites or crustaceans and predatory vertebrates. But during a mussel
census in New Mexico, Todd D. Levine, his graduate adviser at the time,
David J. Berg of Miami University in Hamilton, Ohio, and a colleague
spotted an aggressor unlike any of the others. A nymph of the dragonflyGomphus militaris
was devouring the gills and glochidia of a gravid Texas hornshell. The
team went on to find many similarly damaged gravid (but few non-gravid)
mussels.

It’s unknown how much the insect, in its dual role as parasite (of
female mussels) and predator (of glochidia), affects the Texas
hornshells’ survival. But considering that only two populations of the
mussels are known, the researchers are hurrying to find out.